problems with sync on setup with combination of 2000's and 3000's

I was wondering if you fellas could help me with a problem I am currently experiencing.

I usually use Rekordbox 6.8 (I have also tried the latest version, but that doesn't change this issue). The problem is that when I play on a setup with both the CDJ-3000s and the CDJ-2000NXS2s and DJM 900 NXS ( all on the lastest firmware) , the sync on the 2000s is about half a platter turn behind.

I have already checked the USB, and that doesn't seem to be the issue. When I use a USB from another Rekordbox, I have no problems. However, if I load a track from my database onto that, I experience the same problem, while the old playlist from the other Rekordbox does not have that issue. Everything works fine between the 3000s, but the combination of 2000s and 3000s does not work well. It also doesn't matter where I plug in the USB.